Wavelet-Based Estimation of Site Response

Abstract eng:
Seismic damage is highly dependent on the rate of energy input from the earthquake waves. Ground motions with the same amplitude spectrum can cause substantially different levels of seismic damage on the same structure, depending on the time-frequency localization of the energy imparted to the structure. In this study, a wavelet-based approach to detect nonlinearities and characterize site response is presented. To account for the nonstationary behavior of the ground motion processes, the traditional soil amplification ratio is extended to include the time parameter. The wavelet-based definition of soil amplification factor can easily be compared to its Fourier-based counterpart, by simply taking the root mean square of the time dependent amplification factors, for each frequency. Ground motion records from the main shock and aftershock of the 2001 Nisqually earthquake measured at three sites have been analyzed using Morlet wavelets. The comparison of energy localization patterns observed in the wavelet spectra from different sites is used to detect nonlinear soil behavior and characterize soil damping. Analysis results show the advantage of a wavelet-based approach over its Fourier-based counterpart, where time domain information is lost. This study concludes that the energy localization patterns observed in the wavelet spectra from different sites and events can be used to detect nonlinear effects and characterize soil damping.

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